The use of sealing assemblies which include a T-shaped sealing ring and a pair of back-up or anti-extrusion rings to form a seal between two relatively movable members is generally known. Such sealing assemblies are often used in hydraulic or pneumatic systems for both rod and piston-type seals. The application of T-shaped sealing assemblies to some of these systems has resulted in significant performance advantages over O-ring seal configurations.
U.S. Pat. No. 3,582,094 (hereafter "the '094 patent") discloses a conventional sealing assembly which significantly improved upon the standard O-ring seal configurations. Although the sealing assemblies disclosed in the '094 patent significantly improved upon conventional O-ring seal configurations and perform satisfactorily for most applications, there have been documented isolated instances where the conventional T-shaped seal assemblies have failed in certain relatively high-pressure applications due to resilient tensile stress concentrations from frictional drag yielding degradation of the downstream side of the T-shaped sealing ring. That is, on the atmospheric side of the T-shaped sealing ring, a crack forms in the general area where the radially extending leg intersects the axially extending leg. The crack extends circumferentially around the ring, but not necessarily the full 360.degree.. With dynamic, pressurized activation, the crack then propagates into the body of the elastomeric stem. At some undetermined depth, the crack then exercises open and closed, in such a manner, that segments of rubber break free from the crack edge. This systematic separation of the rubber propagates into a circular pock-mark appearance. In time, the loss of material contaminates the sealing surface which reduces the sealing efficiency. This loss of material also reduces the column strength of the radially extending leg which supports the dynamic crown. As the crown collapses, the radial vector forces are reduced to reduce the compressive sealing stress and results in seal leakage.
In relatively high-pressure applications wherein high performance is required, even isolated instances of failure can be problematic. Thus, a need has arisen for a seal assembly which does not result in pock marks in the area where the radially extending leg intersects the axially extending leg during high-pressure operation.
One seal assembly which attempts to overcome this problem is disclosed in U.S. Pat. No. 3,771,801 (hereafter "the '801 patent"). This seal assembly includes converging side surfaces along the radially extending leg. While the converging side surfaces assist in preventing pock marks in the area where the radially extending leg intersects with the axially extending leg, the seal assembly disclosed in the '801 patent has not provided an effective seal between the first and second members. That is, because of insufficient force applied to the crown and only a small portion of the crown contacting the surface opposed to the groove, during high pressure, the distal end of the radially extending leg achieves rocking motion which results in loss of contact and yields leakage due to the instability. Hence, a need has arisen for a seal assembly which maintains good contact between the first and second members and does not degrade in the area where the radially extending leg intersects the axially extending leg.
The present invention is directed to a seal assembly for sealing a clearance space between first and second relatively displaceable members. The sealing ring of the present invention is generally T-shaped in cross section and includes converging side surfaces on the radially extending leg to prevent pock marks from forming in the area between the radially extending leg and the axially extending leg. The crown of the radially extending leg includes a generally arcuate transition surface in sufficient facing sealed engagement with one of the members to prevent leakage. Accordingly, the sealing assembly of the present invention has a longer life than the seal assemblies of the prior art.